updated August 7, 2004 - The Vo2max is also called the mVo2 test or the CPX test - for cardiopulmonary stress test. This test shows the maximum amount of oxygen your heart can provide to your muscles during sustained activity. Vo2max is the point at which your body cannot increase its intake of oxygen despite an increase in exercise intensity.
Doctors consider this a true measure of your heart's ability to keep you going. In most medical centers, a Vo2max score of 14 (in ml/kg/minute) or less qualifies you for heart transplant. One test result never tells the whole story, of course. My own Vo2 score in 1999 was 13.5 but in 2000 was 20 - without a transplant.
Remember that times will vary a lot from one person to the next and possibly from one test to the next for the same person. You may last 15 minutes or only 3. Your last test may have been 10 minutes but this one may only be 2 minutes long. So don't think of it as a 10 minute test or whatever.

Taking The Test

This test requires special equipment so it is usually done in a lung clinic or hospital. Once in the testing room, you will be asked some questions about your usual activity level, heart failure symptoms and so on - the routine stuff "for the chart." You will be asked to blow into a tube connected to a pulmonologist's (lung doctor's) machine first. This may be done in two ways depending on the setup. Either you will blow once, completely expelling your breath (or you get to do it over and over until you do); Or you will have to blow 5 or 6 times hard and fast with all your lung power into the tube without any rest in between. This method brings me close to passing out, and a lively debate over the wisdom of such methods usually occurs when I have to do this. <g>Then you will have small adhesive electrodes stuck to your chest and sides just like for an EKG. Guys with hairy chests will get some spots shaved for this. The wires attached to these electrodes will connect you to a heart monitor. You will also have another monitor, probably one of the small clip-on types that go on your finger tip. Hey, at least they don't screw the electrodes into your chest anymore like they once did!
There are so many wires involved in monitoring this test that you usually get a "belt" that organizes them all so nothing gets tangled. It's bulky but you can still walk okay with it.

You will stand on a treadmill (sometimes an exercise bike is used) and your blood pressure will be taken with a cuff. Now you get to play "scuba diver!" I have not found a picture of the exact setup my clinic uses but the picture at left is one type in common use. You will breathe only through your mouth into a soft rubbery mouthpiece that you can bite down on to hold in place. My jaws got too tired and I had to hold it up with one hand.
A padded (you hope) clothespin is clamped over your nostrils so you can't breathe except through your mouth. Well, it's not exactly a clothespin but they could save a lot of money using one, for all the difference it would make.
Now the treadmill cranks up and you start them feets awalkin'. The speed will slowly increase until it is as fast as you can manage and we're not talking "comfortable" here - we 're talking about fast. This is a test where they want to push you hard.
As you keep walking, the treadmill will be inclined more and more to increase the difficulty. You will regularly be asked to rate how difficult the walking is for you at that moment. Since you cannot talk with the mouthpiece in, a chart is held up and you point to the degree of difficulty you are feeling.

At least two technicians/nurses should attend you during this test! One will be monitoring you via the pulmonology equipment and the other will be focused entirely on you. He will talk to you before the test and arrange some easy hand signals so he knows how you are feeling. For instance, if you point to your head, it will mean you are getting lightheaded or dizzy. If you point to your feet, it will mean you are extremely fatigued. If you point to your chest, you are having chest pain and so on. He is also gonna catch you if you do something silly, like fall down. No joke. That's why there really must be at least 2 of them right there. That tech may also be taking your blood pressure regularly throughout the test.
The test continues until one of two things happen: Either you simply cannot go on and you signal them to stop the test, or they decide that you have reached the "numbers" that satisfy the doctor's requirements and they stop the test. Unless you are in distress, the treadmill will be slowed down first, rather than abruptly stopped, so you don't get dizzy and fall. Once the treadmill stops, they should place a chair on the treadmill behind you and ease you into it, and let you rest for awhile.
You must keep the mouthpiece in and the clothespin on your nose for a couple more minutes while they get some "cool down" readings and then they can be removed. The electrodes come off, and you're done!
Your doctor will have to discuss the test results and what they mean with you but a rough estimate is that if you have a Vo2max of 14 or less, you may be in line for some treatment changes. Then again, maybe not; it just depends.

Possible Side Effects

Because you are breathing for awhile through only your mouth and you have the mouth piece in, it is almost impossible to swallow during the test. If you do manage to swallow, you will pop your ears big-time anyway. This results in a very dry throat, possibly to the point of pain. Also, because you cannot swallow, you are going to drool. <g> Newer mouthpieces have a built-in catch tube for this but older ones do not. You may feel silly, drooling like a baby, but the techs/nurses are used to it, so don't feel bad. The last thing is, of course, fatigue. You are going to be one tired puppy after this test!

Making It Easier

Don't take your diuretic less than 3 hours before the test. Go pee just before they get started. You will screw up the whole works if you have to stop to go to the bathroom during the test. I do recommend getting a drink of water just before the test to help ease the dry throat you're about to get.
Dress cool and comfortable. Wear your favorite walking shoes. Dress like you're taking a long walk on a summer day and you'll do fine, comfort-wise. Don't eat a big meal first but eat a light meal a couple of hours before the test. I suggest planning on getting something to eat right afterward to restore your energy even if it means taking a "box lunch" with you to the lab or hospital. Have someone else drive you to the clinic or hospital for all this (especially if you drive a clutch) because your legs will be pooped afterward.

February, 2000 - Vo2max testing is important for identifying risk in heart failure patients. However, the best cut-off point to separate those with a poor prognosis from those more likely to survive is not clear. Despite advances, risk for death among patients with severe heart failure remains 30 to 60% annually.
Directly measured Vo2max is more accurate than echo and other exercise tests for predicting 1 to 2 year mortality. It has been reported that heart failure patients with peak Vo2 of 14 mL/kg/minute or higher have a better prognosis than those who don't.
Having a Vo2max less than 14 may indicate a need for heart transplant but to our knowledge there have been no direct comparisons between different peak Vo2 values in CHFers. We tried to find a "best" cut-off point that separates those with a poor prognosis from those more likely to survive.
The study group included 644 patients with advanced heart failure, who had been sent to Stanford for evaluation over a 10 year period. Eighty percent were men, and DCM was the main cause of heart failure (59%). Despite drug therapy, all patients had CHF symptoms and low heart function, with average EF of 20%. Standard medical treatment, including digoxin, diuretics, and ACE inhibitors was given. Many patients were taking Coumadin (46%), anti-arrhythmic drugs (23%), or a beta-blocker.
Four year survival was studied for patients whose Vo2max was below each level, and for those scoring higher than each level. The levels studied were: 10, 11, 12, 13, 14, 15, 16, and 17 mL/kg/min. During 4 year follow-up, 187 patients (29%) died and 101 had a heart transplant. Vo2max was a predictor of survival, a stronger predictor than any other measure. The higher the Vo2max, the better a patient's prognosis. For example, the 3-year risk for death in patients with a Vo2max under 14 was 48%, while risk of death was only 23% in those with Vo2max higher than 14.

Vo2max scores may help decide which patients should continue drug therapy and which should have a heart transplant. A Vo2max of 14 mL/kg/min is currently the recognized cut-off point for transplant. This is based on data that show a Vo2max of less than 14 mL/kg/min means an extremely poor short-term prognosis.
Although using a cut-off such as 14 mL/kg/min appeals to doctors, it has shortcomings. First, it is often difficult to tell what a patient's true heart function limits are or whether disability is also from deconditioning. Second, a cut-off of 12 or 15 may be just as accurate as a cut-off of 14 for identifying patients at risk for death.
Our data suggest that the commonly used Vo2max cut-off of 14 mL/kg/min is not any better than other cut-off points between 10 to 17 mL/kg/min. Any cut-off in this range helps tell which patients are at risk for death, but not how much risk they face.One noteworthy finding is that our data confirm the improving survival rate among patients with severe chronic heart failure in the 1990s. Even in patients with a Vo2max less than 10, 46% were alive at 3 year follow-up. Stevenson reported a 2-year survival rate of 48% for patients with Vo2max less than 10, while we saw a 70% 2-year survival rate in our study.
One weakness of our study is that we used a bicycle to test peak Vo2. Vo2max is higher when a treadmill is used. We conclude that Vo2max should be tested when evaluating heart failure patients. However, we did not find a specific peak Vo2 value that was better for prognosis than any other. This test should be used in combination with other tests to help decide prognosis in heart failure patients.

Vo2Max Low Even In Mild CHF

Introduction - How strongly you can exercise depends partly on your age, but age-adjustment is rarely done in heart failure studies. We studied whether age-adjusted peak Vo2 was reduced in patients with mild heart failure.Peak exercise tests are stopped when the patient feels he can no longer exercise because of shortness of breath or general fatigue. Vo2max tests are done until the technician has enough data to determine actual Vo2max - he tells you when to stop exercising.
Vo2 tests are scored in ml/min/kg. Think of it as measuring how much oxygen is used per minute per 2.2 pounds of body weight. Most general care doctors would call a peak Vo2 score of more than 20 ml/min/kg (Weber class A) normal. In reality, peak Vo2 of 20 is at least 40% under the predicted score in patients younger than 50 years. This shows how important age-adjustment of the peak Vo2 score is.

Weber Classification

class A peak Vo2

more than 20 ml/kg/min

class B peak Vo2

between 20 and 16 ml/kg/min

class C peak Vo2

between 16 and 10 ml/kg/min

class D peak Vo2

less than 10 ml/kg/min

The Test - We measured peak Vo2 and "anaerobic threshold" in 56 men. Anaerobic threshold is the point during exercise that your body can no longer increase its oxygen use even if you work harder, so you get "wiped out" very fast at that point. Anaerobic threshold was closely linked to CHF symptoms in this study..
All patients had an EF between 35 and 55% - average EF was 46%. Fifty were class one and sixteen were class 2. Average age was 52 years. A control group of 17 men with normal EFs also did the same testing.
Testing was done on a bicycle rather than a treadmill. There was a 3-minute warm-up, then workload was increased once per minute. Patients breathed through a mask to allow measuring the amount of air breathed in and out.Peak Vo2 was defined as the average Vo2 during the last minute of the exercise test. "Decreased" exercise capacity was defined as 80% or less than predicted peak Vo2. "Severely decreased" peak Vo2 was defined as less than 62% of predicted peak Vo2.

Results - Both peak Vo2 and age-adjusted peak Vo2 were significantly lower in the patient group, compared to the control group. Seventy-five percent of patients' had a "decreased" age-adjusted peak Vo2 and 18% had a "severely decreased" peak Vo2.
In contrast, only 3 people in the control group (18%) had "decreased" age-adjusted peak Vo2. None were "severely decreased."In general, there was no link between ability to exercise and measured heart function. Class 2 patients had a lower anaerobic threshold.

Discussion - Patients with an EF over 35% may have limited reduced tolerance. We showed that 75% of patients with only mild left heart weakness (EF between 35% and 55%) with little or no CHF symptoms, have reduced exercise capacity; in 18%, exercise capacity is severely reduced.
Doctors should remember that reduced peak Vo2 is not always a sign of heart failure. Lung disease, anemia, muscular or joint problems, or less-than-best effort during exercise testing can cause reduced peak Vo2.In CHFers, many doctors claim that poor physical fitness plays a part in reduced peak Vo2, but we saw a relatively high anaerobic threshold in this study. It would have been lower in physically deconditioned patients. Our results suggest a heart-related cause for reduced exercise capacity.All formulas predicting peak Vo2 indicate that age and sex are important factors. That's why doctors should always adjust results for these factors. Peak Vo2 corrected for age, compared to predicted healthy peak Vo2, may help shape a prognosis in heart failure patients.

Conclusions - Peak Vo2 is significantly reduced in patients with mild left heart failure and few if any symptoms. This group of patients is probably underdiagnosed. Using a Vo2 exercise test to measure age- and sex-adjusted peak Vo2 would be useful in such patients. Anaerobic threshold is more closely linked to heart class than peak Vo2 is, so it may be a better marker for exercise ability.